<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../00-source/jquery.min.js"></script>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        ul{
            width: 500px;
            list-style: none;
            display: flex;
            justify-content: center;
            align-items: center;
            position: relative;
        }
        li{
            height: 50px;
            line-height: 50px;
            text-align: center;
            width: 100px;
            position: relative;
            z-index: 2;
        }
        ul>div{
            position: absolute;
            left: 0;
            top: 0;
            width: 100px;
            height: 50px;
            background-color: gainsboro;
            border-bottom: 2px solid red;
            z-index: 1;
        }
    </style>
</head>
<body>
    <ul>
        <li>1111</li>
        <li>2222</li>
        <li>3333</li>
        <li>4444</li>
        <li>5555</li>
        <div></div>
    </ul>
    <script>
        $('ul>li').mouseenter(function(){
            $('div').stop().animate({
                left:$(this).index()*100
            },300)
        })
    </script>
</body>
</html>